Subatmospheric gas burner



jui? 5, w47. A. R. DUNHAM ET AL 2,424,154

SUB-ATMOSPHERIC GAS BRNER Filed sept. 12, 1940 2 sheets-sheet 1 I and,ura ,l/22500? fag@ WW/'amsm July 15, 1947,. A. R. DUNHAM ET AL.

SUB-ATMOSPHERIC GAS BURNER Filed Sept. 172, 1940 2 SheeLS-Sheet. 2

endl/g Patented '.luly 1.5, 1947 l SUBATMOSPHERIC GAS BURNER Aubra R.Dunham, Glencoe, and Hilding V. Williamson, Chicago, Ill., assignors toExperimental Laboratories Incorporated, Chicago, Ill.. a corporation ofIllinois Application september 12, 1940, serial No. 356,4@

(el. s- 7) 12 Claims.

This invention relates to certain new and useful improvements in a gasburner, more particularly a burner especially adapted for use in agenerator for producing heating medium consisting of a highly saturatedmixture of steam and hot products of combustion for use in a heatingsystem.

A heating system of this general type is shown in the patent to Dunhamet al., 2,046,813, granted July 7, 1936. The uid fuel is burned inproximity to an enclosed body orbodies of water and the products ofcombustion are passed in intimate contact with the water so as to formsteam and the heating medium consisting of the products of combustionyhighly saturated with steam is delivered into radiators wherein thesteam is condensed and a large portion of the heat from the products ofcombustion is used for heating purposes. exhausted from the system thusproducing a partial vacuum and causing the continuous circulation ofheating medium and also maintaining a partial vacuum in the generator soas to draw in the fuel and combustion air. The condensate from the steamis returned to the generator to be reconverted into steam.

The present improved burner is adapted to be mounted transversely withinthe lower portion of the generator and separates an upper combustionchamber from a lower air-supply chamber.

The burner comprises a main lower metallic plate, and a. smallercircular upper plate spaced slightly above the lower plate, and fuel gasis introduced centrally through the lower plate into the space betweenthe plates and iiows upwardly around the edges of the upper plate.Combustion air is drawn from the lower chamber through two concentriccircular series of spaced holes in the main plate so directed that theair jets will meet and supply, together with the gas, a circular amedirected upwardly and inwardly into the combustion chamber. The air andgas are drawn in, in proper proportion, from separate sources each undersubstantially atmospheric pressure, by the vacuum existing in thecombustion chamber.

The principal object of this invention is to provide an improved gasburner of the type briefly described hereinabove and disclosed more indetail in the specifications which follow.

Another object is to provide an improved burner which will not backfire,the air and gas being first mixed at the point of combustion so that thename can be turned down to a minimum.

Another object is to provide improved means for mixing the air and gasso as to more definitely determine and position the flame.

The cooled noncondensable gases are Another object is to provide animproved method and apparatus for properly proportioning and keepingsubstantially constant the rate of fuel and air supply to the burner.

Another object is to provide means for introduc-ing free air around thebase of the flame, for the several reasons hereinafter speciiied.

Another object is to provide an improved pilotflame assembly.

Other objects and advantages of this invention will be more apparentfrom the following detailed description of one approved form ofapparatus designed and operating according to the principles of thisinvention.

In the accompanying drawings:

Fig. 1 is an elevation, largely in central vertical section, of thegenerator with the improved burner installed therein, together with someportions of the heating assembly including the exhauster for maintainingthe vacuum.

Fig. 2 is a vertical central section through the gas now-control valve.

Fig. 3 is a vertical central section through the burner, on a largerscale.

f Fig. 4 is a partial plan view of the burner assembly.

The general heating system will rst be briefly described. Referring lrstto Fig. 1, the generator indicated at A encloses the new burner B in itslower portion, this burner resting on a transverse partition i andseparating the space Within the generator into a lower supply chamber 2and an upper combustion chamber 3. The lower air chamber 2 is enclosedby the lower portion of the outer metallic shell t, and an opening l inthis shell permits the free entrance of air. The gas supply pipe alsopasses in through this opening 5 and may be intermediately supported byany suitable bracket member 1. The upper portion of the combustionchamber 3 is enclosed by a cylindrical'shell 8 having a dome-shaped top9 and an outwardly extending lower flange i0 extending to the shell orhousing Il which holds the water supply. The lower portion of combustionchamber 3 is enclosed by an annular wall l2 of insulating material,within the outer shell t,

except for the opening enclosed by the metallic ,3 I hauster C is inoperation and there is a partial vacuum within combustion chamber 3, thedoor id will be drawn into closed position so that the combustionchamber will be completely closed except for the air inlets through theburner B as hereinafter described. The space I8 within housing I l andsurrounding the inner shell 8 up to the level :l: is filled with water,and the space I9 within housing II above this water level and below thedome-shaped top 20 serves as a mixing chamber for the products oicombustion and steam which flow out through outlet 2I into the supplypipe 22.

The mixing head D serves to conduct the products of combustion fromcombustion chamber 3 into the mixing chamber I3 so as to transfer amaximum of heat to the water, this portion of the apparatus beingdisclosed more in detail and claimed in the patent to Dunham et al.2,169,683, filed August l5, 1939. This head comprises an outercylindrical wall 23 which terminates above the water level x and whichjoins at its lower end with an intermediate horizontal partition 24 fromwhich extends a central cylindrical member 25 enclosing a gas passageleading from combustion chamber 3. A skirt member 28 extendsoutwardlyuand downwardly from partition 24 and terminates somewhat abovethe top 3 of shell 8 so as to permit water to flow into 'the enclosedannular space 21 which becomes more highly heated than the larger bodyof water due to the fact that-it lis largely enclosed by the heatedgases. VAn upper pan member 28 has its central bottom Z9 positionedsomewhat below the water level :c and is supported by a plurality ofvertical pipes or conduits 38 each having its lower and upper open endsttedin the partition 24 and bottom `23 respectively so that water fromthe main body I8 will flow up through these pipes to maintain a normalliquid level at :I: within the pan 33. The upper portion of pan 28 isextended as shown at 3| so that a thin sheet of water 32 will overflowinto the main body of water when the pan is filled as hereinafterdescribed. Another series of vertical conduits 33, similar to theconduits 36 but longer, extend up through the pan 28 so as to dischargejets of water 33 from their upper ends into the domed mixing space i9.

ln operation, the highly heated gases from combustion space 3 will flowup through central passage 25 into the upper casing 23, flowing betweenand around the pipes 30 and 33, and thence out beneath the upper panmember 3l and into the mixing space I3. These gases will highly heat thewater in the annular space 21 and in the pipes 38 and 33 and partiallyboil or vaporize this water so that its density will be reduced and thewater will be forced up to fill the pan 28, and overflow at 32 into themain body of water. Also jets or fountains of water will be thrown up at3d into the mixi g chamber I3 and against the domed top 26. I will benoted that the gases flowing out from beneath the pan 3l will ilowthrough the dispersed liquid 32 and also in con-- tact with the uppersurface a; of the water pool la, while the liquid of jets 34 isbeingdispersed through the heated gases in mixing chamber I3 and againstthe inner surface of dome 20. This tends to cool the dome .and also wetsthe inner surface so as to vaporize and mix with hot dry gases andincrease the heating medium. Also the water surrounding inner shell 8and the mixing head D will be highly pre-heated so that a comuparatively large volume of steam will be quickly formed and mixed withthe combustion gases to form the heating medium that ilows upwardly thetemperature of I ishing the water 4 through pipe 22 to the radiatingsystem. The lower portion of the generator is insulated by the air spacebetween outer shell 4 and inner shell II, although other insulatingmaterial could be used in this space.

The heating medium loses the greater portion of its heat in theradiating system. the steam being condensed and giving off its latentheat, and

the non-condensable combustion gases being considerably lowered. Thecondensate flows back from the radiating system through the pipes 38,31, 38 and 33 into the main body of water I8. It will be noted that thepipe 33 is shown with a central portion broken away, and it is to beunderstood that at this point means (such as shown in the Dunham Patent2,169,683 already referred to) may be provided for replensupply ifnecessary, draining ex cess water and sediment, and maintaining theproper water level a: in the generator. An exhauster or pump C, drivenby motor 43, is connected through piping 4I, 42 and 31 with the returnpipe 36 and through this piping non-condensible gases are withdrawn fromthe radiating system and then discharged from the pump through the ventpipe 43. The vacuum created in the radiators by the condensation ofsteam and by the withdrawal of gases through the venting system by pumpC willcause a partial vacuum extending back into the combustion chamber3, this vacuum serving to draw and fluid fuel, and also to maintain thecirculation of 'heating medium through the Incidentally, this vacuumwill hold the pilot-door I4 closed.

The improved burner B, which forms the particular subject matter of thisinvention, will now be described. This burner 'comprises a main plate 43of generally circular form having an outer horizontal flange 44 whichrests on and is secured to the horizontal partition I in the housing 4,this partition having a central opening corresponding to the generaloutline of plate 43 inside of the flange 44. The plate 43 has a centraldownwardly dished portion comprising the outer inwardly and downwardlysloping wall 45 leading to the horizontal bottom wall 43 having a.central downwardly extending inlet nipple 41 internally threaded at 48to receive the gas-feed pipe 49. The upper edge of sloping wall 45(which extends somewhat above the peripheral ange 44) is connected withii'ange 44 by a short downwardly and outwardly extending flange 58.

A smaller upper circular plate 5I ts within the dished portion of thelower plate, this upper plate II having a. series of ribs 52 extendingradially from a central hub 53, these ribs resting on the upper surfaceof wall 48 of the lower plate so as to space the two plates apart. Theribs 52 serve to divide the stream of gas ilowing in through pipe 43 anddirect this gas equally through the radial passages between ribs 52toward all edge portions of the plate El, around which edges the gasflows upwardly into the combustion chamber. A plurality of threadedstems or bolts 54 provided with wing-nuts 85 project down through theplates so as to hold them firmly in assembled relation. Metallic anchormembers 86 held by the upper end of bolts 54 are imbedded in a covermember 51 of refractory material which is cast over the top of plate 5I,this refractory cover member having rounded edges 58 as shown.

A circular series of equally spaced upwardly directed air holes 58 areformed in the flat cenin the combustion air l radiators.

tamos tral portion 48 of plate l! adjacent the outer periphery of thetop plate li. A second series of inwardly and `upwardly directed airholes 5B are formed in the sloping wall I5. The holes 60 in the secondroware positioned radially outward from the holes 59 in the first row,pair by pair, so that the two jets of air of each pair willconverge andimpinge against one another and, with the gas drawn from between theplates 5| andl 46 form a combustible mixture which will burn with acircular ilame directed upwardly and lnwardly above the centralrefractory member 5l. The iets will impinge at such an angle as to slowdown the nal velocity of the air streams and mix with the gas so thatthe flame will remain substantially xed and will not wander or blow out.

A third row of openings 6l directed upwardly and outwardly are formed inthe narrow inclined wall 56 of the lower plate I3. The air drawn inthrough this outer row oi holes 6l does not directly enter the name atall, but is quite important to the successful operation oi the burner,especially since no combustible mixture is formed until the gas and airare separately drawn into the chamber. This free air from the outer rowof openings tends to stabilize the operating conditions around the baseof the flame. When these outer holes are lacking, ignition takes placeand the llame starts but soon a circulation oi d gases tends to sweepdown and into the base of the name causing the llame to rise up and tendto blow away from the jets. The name will go out in spots and thenreignite with explosive force tending to throw the pilot door it openand then pull it shut with a bang. This action may continue to a pointwhere the entire llame is snuied out, including the pilot flame. Byintroducing sufflcient free air around the base of the llame the aboveaction is prevented. If sui'licient of this free air is introduced, themain flame continues to burn down near the burner, the pilot is notail'ected, and there is no tendency for the name to sputter or blow thedoor open. However, if too much air is brought in around the outside ofthe burner yellow flames will appear. The exact quantity of this freeair desired will vary somewhat with the character of the gas and thevelocity oi.' flame propagation with different gases. This can bedetermined by experience in any given locality and with any particularcharacter of gas. 'I'he lower ends of air inlet holes 5t, to and 0i areall rounded s0 as to facilitate the iniiow of air.

'I'he gas will flow in under city-supply pressure through pipe 82, tothe suction controlled valve B3, which operates as a zero pressureregulator to furnish gas at slightly lower than atmospheric pressurethrough pipe M, metering valve t5, and pipes 8 and 4t to and through theburner B. The metering valve o5 may be a suitable needle-valve and willbe given a flxed manual adjustment which will depend upon the qualityand character of the gas being used.

The valveft comprises an internal `web 66 having a valve opening tl thatmay be closed by ther valve 83 carried by stem' 89 secured at its lowerend to a diaphragm 1i! separating the upper gas chamber il in diaphragmcasing 'l2 from the lower chamber l@ open to the atmosphere at it. Thevalve t3 also includes a loose guide et' for the stem si?. A centeringspringlie enclosed in an upper housing extension lt exerts an upwardpull on the upper end of stem et so as to carry the weight oi theiloating parts. The spring is iii) '.v adjusted so that the valve memberet just barely ialls shut without the aid of gas pressure. The springalso tends to hold the valve centered so as to minimize friction betweenthe valve parts and the valve-seat and guide. When a partial vacuum isdeveloped in the combustion chamber t, this will partially evacuate thepipes te and t5 and reduce the pressure in upper chamber il so that theatmospheric pressure in lower chamber it will force the diaphragm l@upwardly and open valve Se so as to yadmit gas from the supply pipe t2.Obviously. the more valve 68 is opened the greater will be the dow ofgas into the combustion chamber.

This suction controlled valve 63 opens by a slight vacuum from thecombustion chamber and tends to feed gas to the needle valve at asubstantially constant pressure slightly below atmospheric.

The rst step to get proper gas and air ratio control is to reduce thegas pressure in pipe @d to substaantially atmospheric pressure, and thevacuum in the combustion chamber will then be able to draw air from thenormal atmospheric pressure source through the air inlets tit, t@ and tiin the same proportion that it draws gas through the needle valve t5 andthence through the burner. Valve t3 is also a safety valve because theexhauster must be running and creating a vacuum in the combustionchamber before valve 6l will open and any gas can be drawn into theburner.

With the apparatus properly designed and ad@ justed the proportionatenow of air and gas into the combustion chamber will remain substantiallyconstant so as to provide o, proper mixture, although the size of the'dame can be increased or decreased by changing the vacuum in charn-gber t, and within reasonable limits the size of the flame will increaseor decrease to corre spond with the demandsfor heating medium.

Within one side portion of the lower burner plate 43 (preferably theside adjacent the door it) is formed a depressed well ll for housing thepilot burner B. This pilot burner eorn= prises a small gas jet it soinclined that the naine it (Fig. l) will project inwardly suiiloient toignite the main burner when the combustible mixture is owing. At thesame time this jet 'itl is housed withinthe well il so that the jet willnot blow out when che door it is opened. When the main burner isextinguished and the exhauster C is not operating, that is when thevacuum is broken in chamber t and the heat-s ing medium is no longercirculating, the door id will :all open (see Fig. l)4 and the gases fromthe pilot-burner can vent through this door opening. In this way thepilot-burner can continue in operation at all times. In the example hereshown, a thermo-couple et is positioned adjacent the pilot-burner le,this thermo-couple acting, when heated. to hold open e supply valve inthe :main fuel-pipe. ln case the pilot burner should be extinguished thethermo-couple t@ wiil cool off and permit this kvalve to close. Thecable 8l leading from the thermo-couple to and the gas supply pipe t2for the pilot-burner may conveniently enter 11e generator through theair inlet opening b.

This improved burner will not backfire since the gas and air enter thecombustion chain separately and are not mixed until they reachsubstantially the point of combustion, conse silently the burner can beturned down to minimum. By using a number oi small inist air holes ororifices producing forceful air iets which inspirate the gas, a bettergas and air mixture is obtained `which gives a shorter hotter flame andmakes it possible to use a smaller combustion chamber. By arrangingthese small jets in a circle, ignition starts at one side and movesaround rapidly but not with the explosiveness that wouldresult if allthe gas and air were introduced at one point with a single jet. Byarranging the combustion air jets in pairs which strike one another soas to create eddies, the flame is held in place and the increasedturbulence tends to mix the air and gas and improve the mixture so thatcombustion takes place almost instantly. The gas and air are bothpre-heated to some extent in passing through the burner orifices thusaiding in combustion. The burner plates 43 and 5I are preferably made ofaluminum so that heat will -be drawn down to pre-heat the combustionmaterials, but the refractory covering l on the upper plate serves toprotect this portion of the burner from too much heat. This refractoryplate also creates a central hot zone Where combustion can take placewith the best results.

This apparatus is adapted to operate under a rather small vacuum, but agreater vacuum than natural draft will as a rule produce. Such a systemhas the advantage that there is no outward leakage. It will also benoted that while the usual gas burner operates by inspirating thecombustion air into the gas which enters under pressure, in the presentburner the combustion air jets are drawn or sucked into the burner andthe gas is inspirated into the mixture by the force of the air jets.There will never be an excess of fuel since the gas is drawn in by theair and is also controlled by a cut-off valve responsive to the degreeof vacuum within the combustion chamber. It will also be noted that thisimproved burner can readily be used as a. conversion burner unit inexisting boilers or heating plants by transversely sealing this burnerwithin the combustion space and installing a suction or exhaust meansacting on the stack or vent.

We claim:

l. A gas burner comprising a main metallic,

plate adapted to separate an air-supply chamber from a combustionchamber, said plate being centrally dished so that the plate comprises acentral substantially circular horizontal portion surrounded by anupwardly and outwardly sloping rim extending to a main outer horizontalportion, an upper substantially circular metallic plate havingdownwardly projecting radial ribs which rest on the flat-central portionof the main plate within the dished recess and support the upper platein spaced position above the main plate, the

main plate having an opening in its central portion for receiving gasfrom a supply-pipe said gas flowing outwardly between the radial ribsand upwardly around the circumferential edge of the upper plate andcover, a circular series of upwardly directed air-holes adjacent theedge of the upper plate, and a second concentric circular series ofupwardly and inwardly directed airholes formed in the upwardly slopingrim of the dished portion of the main plate so that the air from theseholes will implnge against the air from the inner holes and combine withthe gas to supply a circular flame projecting upwardly and inwardly intothe combustion chamber.

2. .A gas burner comprising a main metallic plate adapted to separate anair-supply chamber from a combustion chamber, said plate being plate, acovering of refractory material mounted on the upper surface of theupper circular plate; the main plate having an opening in its centralportion for receiving gas from a supply-pipe said gas flowing outwardlybetween the radial ribs and upwardly around the circumferential edge ofthe upper plate and cover, a circular series of upwardly directedair-holes adjacent the edge of the upper plate, and a second concentriccircular series of upwardly and inwardly directed airholes formed in theupwardly sloping rim of the dished portion of the main plate so that theair from these holes will implnge against the air from the inner holesand combine with the gas to supply a circular flame projecting upwardlyand inwardly into the combustion chamber.

3. A gas burner comprising a main metallic plate adapted to separate anair-supply chamber from a combustion chamber, said plate being centrallydished so that the plate comprises a central substantially circularhorizontal portion surrounded by an upwardly and outwardly sloping rimextending to a main outer horizontal portion. an upper substantiallycircular metallic plate having downwardly projecting radial ribs which'rest on the flat-central portion of the main plate within the dishedrecess and support the upper plate in spaced position above the mainplate, the main plate having an opening in its central portion forreceiving gas from a supply-pipe said gas flowing outwardly between theradial ribs and upwardly around the circumferential edge of the upperplate, a circular series of upwardly directed air-holes adjacent theedge of the upper plate, a second concentric circular series of upwardlyand inwardly directed air-holes formed in the upwardly sloping rim ofthe dished portion of the main plate so that the air from these holeswill implnge against the air from the inner holes and combine with thegas to supply a circular flame projecting upwardly and inwardly into thecombustion chamber, and a third outer concentric series of air holes inthe upper outer flat portion of the main plate and directed upwardly andoutwardly.

4. A gas burner comprising a main metallic plate adapted to separate anair-supply chamber from a combustion chamber, said plate being centrallydished so that the plate comprises a central substantially circularhorizontal portion surrounded by an upwardly and outwardly sloping rimextending to a main outer horizontal portion, an upper substantiallycircular metallic plate having downwardly projecting radial ribs whichrest on the at central portion of the main plate within the dishedrecess and support the upper plate in spaced position above the mainplate, a covering of refractory material mounted on the upper surface ofthe upper circular plate, the main plate having an opening in itscentral portion for receiving gas from a supply-pipe said gas flowingoutwardly between the radial ribs and upwardly around thecircumferential edge of the upper plate and cover, a circular series ofupwardly directed air-holes adjacent the edge of the upper plate, asecond concentric circular -to be positioned transversely in a housingso as to separate a lower air-inlet chamber from an upper combustionchamber, -said assembly comprising a main metallic plate, asubstantially circular upper burner plate supported on and spaced fromsaid main plate by a plurality oi substan- 4vtially radial ribaand meanscommunicating with the central portionv of the space between the platesfor supplying gas thereto under substantially atmospheric pressure,there being a'substantially circular series of upwardly directedair-openings formed through the main plate and leading from the airinlet chamber into the com'- bustion chamber at locations adjacent theouter edge of the upper plate so that jets ot air directed upwardly fromthese openings will draw gas from between the plates into the combustionchamber, and means including a conduit communicating with said airopenings for creating said upwardly directed air jets.

6. In combination, a burner assembly adapted to be positionedtransversely in a housing `so as to separate a lower air-inlet chamberfrom an upper combustion chamber, said assembly comprising a' mainmetallic plate, a substantially circular upper burner plate supported onand spaced from said main plate by a plurality oi substantially radialribs, a top covering of refractory material on said upper plate, andmeans communicating with the central portion of the space between theplates tor supplying gas thereto under substantially atmosphericpressure, there being a substantially circular series of upwardlyvdirected air-openings iormedthrough the main plate and leading from theair inlet chamber into the combustion chamber at locations adjacent theouter edge oi the upper plate so that jets of air drawn upwardly throughthese openings will now across the space between the plates to draw gasfrom said space into the combustion chamber, and suction means includinga conduit com municating with said air openings for drawing said jets ofair upwardly therethrough.

7. In lcombination, a. burner assembly adapted to be positionedtransversely in a housing so as to separate a lower air-inlet chamberfrom an upper combustion chamber, said assembly comprising a mainmetallic plate, a substantially circular upper burner plate supported onand spaced from said main plate by a plurality of substantially radialribs, and means communieating with the central portion oi the spacebeforced upwardly through both series of openings will impinge againstone another to retard their rate of movement and f orm with the gasdrawn from between the plates a circular flame projecting upwardly andinwardly into the combustion chamber above the upper plate and suctionmeans communicating with said air openings for drawing air upwardlytherethrough.

8. In combination, a burner assembly adapted to be positionedtransversely in a housing so as to separatea lower air-inlet chamberfrom an upper combustion chamber, said assembly comprising a mainmetallic plate, a substantially circular upper burner plate supported onand spaced from said main plate by a plurality of substantially radialribs, and means communicating with the central portion of the spacebetween the plates for supplying gas thereto under substantiallyatmospheric pressure so that this gas will ilow evenly between the ribsinto the combustion chamber, therebeing a substantially circular serieslof upwardly directed air-openings formed through the main plate andleading into the com. bustion chamber at locations adjacent the cir-fcumference of the upper plate a second series oi air-openings'concentric with the irst series and tween the plates for supplying gasthereto under substantially atmospheric pressure so that this gas willilow evenly between the ribs into the combustion chamber, there being asubstantially circular series of upwardly directed air-openings formedthrough the main plate and leading into the combustion chamber atlocations adja cent the circumference oi the upper plate, a secondseries of air-openings concentric with the irst series and being spacedoutwardly in radial alignment with and inclinedtoward the open= inge orthe nrst series so that the air streams being spaced outwardly in radialalignment with and inclined toward the openings of the ilrst series sothat the air streams forced upwardly through both series of openingswill impinge against one another and form with the gas drawn frombetween the plates a circular llame projecting upwardly and inwardlyinto the combustion chamber above the upper plate. there being a thirdcircular' series of air-openings through the mainfplate, outside-oi thesecond series. and directed upwardly and outwardly and suction means fordrawing air upwardly through said air openings. l

9. In combination, a gas burner comprisinga main plate adapted toseparate an air supply chamber from a combustion chamber andV includinga centrally dished circular portion having a nat bottom portionconnected by an upwardly sloping wall to an outer horizontal. flangeportion, 'an upper plate arranged in the dished portion of the mainplate and having downwardly projecting radial ribse-wlnch rest on theflat bottom portion oi the marrlate and denne shallow passages fordirecting gas from a central supply. opening to the outer edge of theupper plate,y

means for delivering gas into said shallow passage at substantiallyatmospheric pressure there being a series oi upwardly directed air holesformed in the main plate adjacent to the edge or the upper plate so thatupwardly directed thereof and to mix therewith, and means for causingvsaid streams of air to ilow from said air holes. l

l0. En combination, a gas burner positioned transversely in a housing soas to separate a lower air inlet chamber from an upper combustionchamber, there being a gas inlet passage in the burner for deliveringgaslaterally at a location above the bottom of the burner. means assise1l for vdelivering gas to said las inlet passage at substantiallyatmospheric pressure and the burn er having also concentric rows ofupwardly di- "rected air openings, the inner row of which is positionedbelow the gas inlet, whereby Jets of air directed upwardly from said airopenings across said inlet withdraw gas therefrom to form an aeratedgaseous mixture, and another row of said air openings being positionedwith their axes inclined in a direction toward the iirst'inenV tionedrow of openings, whereby the air jets from said concentricrows ofopenings impinge at a location above the gas inlet to reduce their veiocity and eilect further aeration ot the mixture, and suction meanscommunicating through said housing with said air inlet openings fordrawing said iets of air upwardly therethrough 1l. In combination, aburner assembly having a gas inlet passage therein and a series of airinlet openings positioned to direct .iets of air across the dischargeend oi the Zas passage, means for delivering gas to said gasinletpassage at substantially atmospheric pressure, and air jetproducing means communicating with said air openings for forcing jets ofair therefrom, whereby the gas is withdrawn from said passage by theinspirating action of the air jets; the 'sumeer assembly being alsoprovided with. a second series of air openings communicating with seidair jet producing means and inclined toward the tlrst mentioned seriesof openings so that the air jets from the second series of airopeninssinr pinge against the jets from the first mentioned series ofopenings to retard the velocity thereof and spread thegaseous mixture ata location beyoud the ses passage.

l2. In a heat generator in which a partial vacuum created in the upperportion oi' the gener-' ator creates a suction to draw air and fuel intoa combustion space thereof; a casing enclosing; said combustion. spaceand an air supply chamber andhaving a door opening leading into saidcombustion space; a closure for said opening pivotally supportednormally in a partially open position and adapted to be drawn to aclosed f ens le. newness.

REFERENCES @li'liib The following references are oi record 'me of thispatent:

D STATES

